The relationship of analgesic tolerance and a morphine-induced change in rat brain chromatin will be investigated. These studies will include (1) the localization of the brain chromatin effect by cell type and brain area; (2) the characterization of the chromatin effect by identification of changes in histone and nonhistone proteins; (3) identification of RNA changes using RNA-DNA hybridization; and (4) the examination of morphine binding to RNA synthesized on chromatin from tolerant rats.